Dan House: This Benji mod is for you!

Dan House: This Benji mod is for you!

Joined: April 1st, 2009, 3:18 am

August 15th, 2011, 2:02 am #1

Okay guys. Today the Benji 392/392 mod is a full length 7/8" diamter barrel that protrudes two inches past the tube (may trim a little more off).

What was done: Two telescopic brass tubes are used. The first tube that slips over the factory tube is 11/32 I.D. by .014 wall. The next tube is a 7/16" O.D. (thick walled) that is a telescopic fit over the 11/32" tube.

A slot on both tubes needed to be cut along the entire lengths. As each tube is applied, the slot needs to be cut wider to accomadate for the radius gains. The slot ends at the muzzle. The final tube is soldered in place, of course.

What does this do? Allows for "devices" to be used.

The larger diameter 'barrel' now has a much wider solder base along the pump tube which adds a great deal of strength to the overall design. used was 380-420 degree solder lead-tin mix, rather low heat stuff because I did not want to fudge the factory solder joints or risk having things come apart.

The end plug needed (of course) a small radius/indent added that matches the amount of barrel that now falls below the front plug (overlapping effect of the barrel in relation to the tube). All is in a perfect straight line - perfect alignment - looks liek a factory job.

Oh, that black thing leaning against the wall? That is the barrel assembly for a three-barreled paintball minigun I am almost finished with...





"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

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Joined: March 1st, 2002, 12:22 am

August 15th, 2011, 2:53 am #2


I did a similar mod on the first go round with the AC build up. I only used one tube, slotted as you described. I didnt want a longer gun, so I wacked 2 inches off the barrel. Gave space for the internals. Epoxied it on.

Warning: properly applied, epoxy can be stronger than the solder joint. (which is how I got a donor pump tube)

I assume that the breach end of this assembly is butted up against the breach and made to fit flush?

Very cool, and creative. Still have off center/eccentric internals? Shouldnt be an issue (hehe for you anyway )? or you got something in mind to solve that little snag?

 


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Joined: April 1st, 2009, 3:18 am

August 15th, 2011, 3:41 am #3

Off center? The added tubes are slotted, but the muzzle end of the tubes are in line with the barrel/muzzle. Yeah, each tube was reamed with an 82 degree reamer at the breech end to slip up on the taper of the breech a little. I didn't chop the barrel or anything, just removed the front sight. Surprised me! Fell right off once it got hot. Had the muzzle pointed down when heating.

Not really a shroud, makes the barrel thicker though, and allows for things to be added to the muzzle. Suppose I could "cap" off the 2 inches of added tube with tube cap w/hole in the middle. Then stack a series o-rings and washers on that 2 inches to see if a mini moderator is made. A pre-stage for the final stage of my licensed silencer...

The other good thing is that the Crosman scope mount bases should work for this setup.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

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Joined: March 1st, 2002, 12:22 am

August 15th, 2011, 3:57 am #4


off center, the bore will not be centered in the tube.

<img border="0" alt="Photobucket" src="http://img.photobucket.com/albums/v301/ ... muzzle.jpg"> 

my first go round on for shrouding the 397. Because the shroud indexes on the glue joint, its off center relative to the bore.

 


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Joined: April 1st, 2009, 3:18 am

August 15th, 2011, 4:01 am #5

Yeah, mine is in line. No offset. Is the 397 bore not cntered in the barrel on the 397?? Never owned a .177 cal version.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

Last edited by Duane30 on August 15th, 2011, 4:07 am, edited 1 time in total.
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Joined: March 1st, 2002, 12:22 am

August 15th, 2011, 4:07 am #6


of the tubintg to be inline with the bore center line?

hmmmmm.

How do you intend to mount the scope? Assuming youre going to.....

 


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Joined: April 1st, 2009, 3:18 am

August 15th, 2011, 4:12 am #7

Let me see if my cell phone can do a better pic, or pics...

I assume the Crosman intermounts will now work since the barrel is 7/16" diamater now. Did have a set, but traded them off a while back...

Be right back!

Notice the end plug. There is a slight radius removed equal to that of the tube. The removed portion is only as thick as the lip on the plug.

You can see my sweet solder job! Yeah, I am self centered on it! My first attempt at soldering on a Benji and it went too well!! You will also notice how the added tubes mate up evenly and centered on the breech taper.

I measured all the tubes (diameters), even the pump tube, then crunched the math as to how much the tube will need to be removed each time a tube was added, as the barrel got thicker by the layers.

My only question is if the head annealed the metal or not (?). Next, it will be media blasted then a nice coat of gray (or grey) appliance epoxy for that parkerized look. Any better ideas on paint?



Last edited by Duane30 on August 15th, 2011, 4:46 am, edited 1 time in total.
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Joined: March 1st, 2002, 12:22 am

August 15th, 2011, 4:14 am #8

Yeah, mine is in line. No offset. Is the 397 bore not cntered in the barrel on the 397?? Never owned a .177 cal version.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

reread your response.... no the barrel and bore ARE concentric

But slotting the tube and sliding it over the solder joint creates an asymmetrical space in the shroud tube. center line of the shroud is above the center line of the bore, eccentric.

which makes internals,,,, infernal.....

cant tell you how many bits have been blown out thefront from misalignment

  

 


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the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
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Joined: March 1st, 2002, 12:22 am

August 15th, 2011, 5:01 am #9

Let me see if my cell phone can do a better pic, or pics...

I assume the Crosman intermounts will now work since the barrel is 7/16" diamater now. Did have a set, but traded them off a while back...

Be right back!

Notice the end plug. There is a slight radius removed equal to that of the tube. The removed portion is only as thick as the lip on the plug.

You can see my sweet solder job! Yeah, I am self centered on it! My first attempt at soldering on a Benji and it went too well!! You will also notice how the added tubes mate up evenly and centered on the breech taper.

I measured all the tubes (diameters), even the pump tube, then crunched the math as to how much the tube will need to be removed each time a tube was added, as the barrel got thicker by the layers.

My only question is if the head annealed the metal or not (?). Next, it will be media blasted then a nice coat of gray (or grey) appliance epoxy for that parkerized look. Any better ideas on paint?



so let me repeat it back to ya....

the changes in ever increasing barrel diameter are accounted for in the slot width

the slot width lets the tubes set down low enough to keep their center line aligned with the bore

the slot stops at or around the muzzle, releiveing the end plug allow the tube to stay concentric to the bore

and now "standard internal designs" can now be created.

What did you say the extra length was? 2 inches?

So thats the trade off: short gun= eccentric shroud, longer gun allows concentric SSR efforts.....

 


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the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
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Joined: April 1st, 2009, 3:18 am

August 15th, 2011, 5:12 am #10

The pics clear up by resizing them smaller (Control and - buttons).

I was confused for a moment... Long day.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

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